Harvesting

One of the most rewarding things about growing algae is harvesting it.  I will bet you a dollar that when you harvest your first one, you will think “Green Gold”!   There are several ways to get biomass out of water, here is a rundown of the ways we suggest:

Filtration: (favorite)

The easiest way to harvest algae is to filter it!   This assumes a few things, first the algae have to be large enough to be screened out and secondly, you need a screen with a tight enough mesh to catch the algae.  

The tightest meshes are in the 30uM range, so that means that you need to have an algae strain that is larger than 30uM.  Our only strain that is easily filtered out is spirulina.  Spirulina is a giant in the microalgae world with trichomes (colony) lengths from 20uM to 1,000uM.  Yes, that means that you can see them with your naked eye!!!

Here is the Algae Research and Supply Spirulina Harvesting screen.  It works for spirulina and for zooplankton (brine shrimp and copepods).

Sedimentation

The lazy-person’s way to harvest algae is to sediment!  Here, you cause or let the algae to fall to the bottom of the tank, then you decant off the clear water on top, finally collect the concentrate at the bottom.  Chlorella is very compliant with this process, when it is ‘ripe’ it simply falls to the bottom. Nannochloropsis, on the other hand, has very negatively charged cell surfaces, so they repel each other and sinking is not rapid, even when the nutrients have been used up.  

Centrifugation

Brute force is what drives the cells from the water using a centrifuge.  A centrifuge can add 15,000x the force of gravity to shove the slight more dense algae cells to the bottom of the centrifuge.  There are many different types of centrifuges:

Lab bench top:  Great for small volumes, generally 50mL tubes.  

Flow through :  Algae/Water mix/slurry is fed into the top port with gravity or low flow pump. The centrifuge force settles the algae, trapping it in the bowl, under the lip. Out spins clean water. Once the centrifuge is stopped, the liquid contents in the bowl will drain out of the sump. Here is a link to a friend of our who manufactures flow through centrifuges:  AlgaeCentrifuge.com

Decanter Centrifuge: A decanter centrifuge (also known as solid bowl centrifuge) separates continuously solid materials from liquids in the slurry, and plays an important role in the wastewater treatment, chemical, oil, and food processing industries.